A. Field of the Invention
The present invention relates to methods and apparatus for detecting and abating leaks of flowing liquids from pipes in buildings and similar structures. More particularly, the invention relates to a method and apparatus which uses differential flow rate sensors for detecting water leaks, particularly in closed loop water circulation systems, and solenoid valves to shut off water flow if a detected leak rate exceeds a predetermined value.
B. Description of Background Art
Contemporary buildings of various types, and particularly hospitals, institutional buildings, and larger commercial and industrial buildings employ a variety of water distribution piping or plumbing systems. Thus, in addition to plumbing used to supply potable water for consumption by the building' occupants, highly purified water for use in production processing, or lower quality water for other purposes, many larger contemporary buildings also have at least one of the following two additional types of water distribution systems through which water is circulated, but infrequently discharged. One such water circulation or distribution system, which may be referred to as a “closed-loop” or closed-cycle system is used to supply water to ceiling-mounted fire extinguisher sprinkler heads. Obviously, water conveyed through plumbing of a building water supply system to fire sprinkler heads is discharged from the system rarely, that is, only in the event of a fire, or during periodic testing of the fire sprinkler system and sprinkler heads.
A second type of closed-loop water circulation system used in many larger contemporary buildings comprises part of the Heating, Ventilating and Air Conditioning (HVAC) system of the building. In particular, some larger buildings including hospitals use hot water as a primary working fluid to heat various regions or zones of the building to different individually controllable temperatures. The hot water is generated by a boiler which is generally located in a basement of the building, or in another structure which houses the “mechanical plant” of the building adjacent to the building. The hot water is typically circulated in a continuously, closed loop cycle, which originates at the hot, discharge side of a boiler heat exchanger.
Heated water issued from the discharge side of a boiler heat-exchanger is pumped upwardly through a vertical hot water source (HWS) riser pipe to the highest building floor requiring heating. At each location or zone of a building which requires heating, the hot water is input to a box-like heat exchanger terminal, such as a Variable Air Volume (VAV) terminal. Within the VAV terminal, air from an external source which is moved by an external or internal blower or fan is directed to flow in contact with the exterior surfaces of a coiled length of tubing called a heater coil which has an inlet port fitting which is connected to and receives hot water from the hot water source riser pipe.
The heater coil functions as a flowing air to hot water heat exchanger, and heats the air which flows through the heater coil. The flowing air is heated to a temperature which is adjusted by a thermostatically controlled fan and/or a damper valve for varying the volume of temperature controlled air which is discharged from the VAV terminal and conducted through ducts to ceiling diffusers or other outlet ports in various rooms of a building. Cooled water from the discharge side of the heat exchanger coil is conducted back down through a hot water return (HWR) riser line to the cold inlet side of the boiler heat exchanger. Thus, in such a system, a fixed volume of water is continuously circulated through the system, and is not discharged.
As can be well imagined, heating systems of the type described above, when used in large buildings with many zones and associated heat exchanger terminals, typically include a substantially large number of individual pipes, tubes and fittings. Thus there is the possibility of a leak developing at many different locations in the closed-loop system, the probability of which is increased in the event of seismic disturbance of the building. Therefore, it is understandable that prudent building maintenance procedures would necessitate monitoring such closed-loop water circulation systems for leaks, and providing an alarm signal to building maintenance personnel in the event of a leak. Also, it would be desirable to provide a method and apparatus for automatically shutting off flow of water if a leak is detected.
Regarding first the problem of detecting a water leak, there are of course a large variety of water leak detectors which employ sensors that utilize a supply voltage and a pair of electrodes to detect electrically conductive water which has leaked onto and bridged the sensor electrodes. However, such electrolytic water leak sensors are effective only in detecting water leakage at discrete locations where the sensors are placed. Such point sensors would be for detecting leaks in most closed-loop water circulation systems, such as an HVAC hot water circulation system of the type described above. This is because a water leak detection system using point sensors for systems such as closed-loop water circulating systems which extend over a large area would require an unreasonably large number of individual sensors which were placed near every possible leakage point.
That the detection and abatement of water leaks in contemporary buildings is an important problem is evidenced by two recent cases in California, where leakage from broken building hot water circulation systems caused more than one million dollars worth of damage in each of the buildings. Part of the expenses associated with water leaks in buildings results from modern building codes and potential legal liability which require the complete removal and replacement of all drywall that has been subjected to water leaks for more than 72 hours, to prevent the growth of molds which can cause health problems.
More important than potential financial losses which can result from water leakage that is not timely detected and abated is the possibility of serious injury or even death which can result if a leak in a hot water circulation system of a hospital building should occur. For example, a hot water leak may allow sufficient water to accumulate, leak through ceilings and scald patients in their beds on lower floors.
The foregoing considerations of potential financial losses, bodily injuries and even deaths which may result from water leaks in modern buildings, and the unavailability of an adequate solution to the problem of promptly detecting leaks and shutting off water flow in closed-loop water circulation systems prompted the present invention.